Attritioning of carbon black

ABSTRACT

Carbon black structure is reduced by grinding the black in a ball mill. The grinding rate is increased and the grinding energy requirement is reduced by moistening the black with oil. The proportion of oil to carbon black is generally within the range of about 5 to about 100 parts by weight of oil per 100 parts by weight of black.

United States Patent Richard E. Driscoll Monroe; Charles H. McCallum,Swartz, both of, La. 15,924 Mar. 2, 1970 Aug. 31, 1971 Cities ServiceCompany New York, N.Y.

[72] Inventors [21 App]. No. [22] Filed [45] Patented [73} Assignee [54]ATTRITIONING OF CARBON BLACK [56] References Cited 5 UNITED STATESPATENTS 2,453,557 11/1948 Voet 241/21 x 3,565,659 2/1971 Dickerson 241/5x Primary Examiner-Granville Y. Custer, Jr. AttorneyrvJ- Richard Geamanand Elton F. Gunn ABSTRACT: Carbon black structure is reduced bygrinding the black in a ball mill. The grinding rate is increased andthe grinding energy requirement is reduced by moistening the black withoil. The proportion of oil to carbon black is generally within the rangeof about 5 to about 100 parts by weight of oil per 100 parts by weightof black.

. A'ITRITIONING OF CARBON BLACK BACKGROUND OF THE INVENTION Carbonblacks are characterized by a physical property known as structure,which can be generally described as a linking together of the particlesinto a chain during formation of the black. High structure blacks arecharacterized by the presence of long, extensively developed chainswhile low structure blacks exhibit little or no linking together e.g.the particles. Both high and low structure carbon blacks are useful,each type being suitable for different applications. High andintermediate structure blacks are made primarily by oil furnaceprocesses while low structure blacks are produced by the thermaldecomposition of natural gas in channel or thermal black processes. Inrubber, carbon black structure has a significant effect upon theresultant modulus of the compound, i.e. modulus development will berelatively high or low in direct proportion to the structure level ofthe black. In most instances structure is measured by the liquidabsorptive capacity of the black, e.g. linseed oil or dibutylphthalateabsorption, since structure development can be directly related to thismeasurement.

It has recently been discovered that carbon blacks having desirablephysical and chemical properties can be produced by the severeattritioning of blacks which have either high or intermediate structure.By means of such treatment the carbon structure chains can be broken upto a considerable degree, and the chemical activity of the black canalso be enhanced since the number of active sites on the surface of theparticles is increased by fracture of the chains. By heavy attritioningof intermediate or high structure oil furnace blacks,

modified carbon blacks can be produced which resemblechannel blacks, andwhich are therefore useful as substitutes for channel blacks in certainrubber compounds. Because of the high surface activity of these blacks,they sometimes'impart performance to rubber which is superior to orunavailable from channel blacks.

It is known that the structure of carbon black can be reduced by passingthe black through tightly compressed steel rolls, or by means of rotaryor vibrating ball mills wherein the black is attrited by means of impactwhich occurs between rapidly moving steel balls. Although ball millingpresently represents the best known approach to the mechanical reductionof carbon black structure, this method has nonetheless suffered from thedrawback of insufficient grinding rate to the extent that it is largelyuneconomical, i.e. the time and energy requirements for grinding theblack to the desired level of reduced structure have been too great.

SUMMARY OF THE INVENTION It is therefore an object of this invention toincrease the rate at which carbon black can be ground in a ball mill.

Another object of this invention is to reduce the amount of energyrequired for grinding carbon black in a ball mill.

Even another object of this invention is to produce a carbon blackhaving reduced structure by the ball milling of a structured carbonblack.

Other objects and advantages of this invention will become apparent fromthe following description and the appended claims.

Heretofore, carbon black has been ground in a ball mill in either asubstantially dry or a substantially wet state; i.e. while having awater content of less than about 20 percent by weight ,or considerablyin excess of about 100 percent by weight. In the case of dry grinding,the bulk density of-the carbon black being ground is not substantiallyincreased and the black particles are subject to being thrown about as aloose dust within the grinding chamber. As such, it is difficult toentrap and crush the dispersed carbon black particles between thegrinding media, and the grinding efficiency of the mill is thus quitelowxIf, on the other hand, large quantities of water are mixed with theblack to the extent that a resilient paste or viscous slurry is formed,movement of the grinding media is considerably dampened and too much ofthe grinding energy is dissipated into the water rather than into thecarbon black. In addition, it becomes necessary to remove excessivelylarge amounts of water from a paste or slurry of carbon black when it isdesirable that the finished product be in a substantially dry form.

In accordance with the present invention, the carbon black being groundis moistened with a rubber-processing oil to the extent that theparticles are formed into a dense, powdery mass which can be furtherdescribed as nondusting but which on the other hand is not so wet withthe oil as to form a paste or slurry of the black. Accordingly, thegrinding efficiency of the ball milling operation is greatly increasedsince the oil moistened particles can be acted upon to maximum advantageby the attritive forces of the grinding media, e.g. the rate of grindingcan be increased several fold and the amount of energy required to grindeach pound of black can be greatly reduced at theisame time.

Generally, the proportion of rubber-processing oil to carbon black whichcan be used for carrying out the invention will fall within the range ofabout 5 to about I00 parts by weight of oil per parts by weight ofcarbon black, but other proportions can be employed provided thatdusting in the ball mill is significantly reduced without forming apaste or slurry of the black. Usually, the oil is not removed from thecarbon black after the grinding thereof, but is left on the surface ofthe particles to become an ingredient of a rubber compound into whichthe ground black is incorporated. In such a case, the proportion of oilemployed in grinding the black can be the same as is called for in therubber compound; e.g. frequently from about 5 to about 50 parts byweight of oil per 100 parts by weight of black, although largerproportions of oil can also be employed.

The type of rubber-processing oil which can be used in the practice ofthe invention is subject to considerable variation since it may beselected from a wide variety of the so-called extension oils,plasticizing oils, and processing aids which may be, for example, anapthenic petroleum oil, an aromatic petroleum oil, a paraffinicpetroleum oil, a low molecular weight polybutene or a vegetable oil. 7

The type of ball mill that is employed for grinding of the black is notessential to the invention since the grinding rate and/or energyrequirements can be reduced with any given type. It will be understoodthat the term ball mill as used herein is intended to mean any grindingmill having an enclosed milling chamberthat is partially filled withhard surfaced objects (the grinding media) such as balls, pebbles, rods,and the like, and whereupon moving the chamber the hard surfaced objectsare caused to forcefully collide with one another so that the materialbeing ground is to the attritioning effect of heavy impacts betweenobjects. It will be appreciated that vibratory ball mills can beemployed to advantage in the practice of this invention since theyprovide a grinding rate which is generally much faster than that whichis available from a rotary mill.

DESCRIPTION OF PREFERRED EMBODIMENTS EXAMPLE I An intermediate structureI-IAF oil furnace black having a Stiff Paste Oil Absorption value of13.2 gal./ 100 lbs. was ball milled in order to provide an attritionmodified oil furnace black which could be used as a substitute for EPCchannel black as a rubber reinforcing pigment. The I-IAF black wasground dry and also in accordance with the invention using a vibratingball mill having a grinding chamber with a diameter of 15 inches and alength of 18 inches. The grinding media (steel balls) consisted of 70pounds of balls, 35 pounds of -inch balls, pounds of 34-inch balls andI05 pounds of linch balls. Vibration frequency was 1,140 vibrations perminute; vibration amplitude was ii-inch. Conditions and results of thegrinding operations is shown in table I.

In the runs made in accordance with the invention, i.e. using 10 and 20parts by weight of oil per 100 parts by weight of black, the oil was anapthenic petroleum oil (Circosol 42XH) which was sprayed onto a bed ofthe black, with gentle agitation, prior to passing the black to andthrough the ball mill. As can be seen from table 1, grinding the carbonblack in ac cordance with the invention provided reduction in thestructure of the black at a much faster rate. More specifically,reduction to a l0.7 gal/100 lb. oil absorption level was accomplished inonly one pass through the mill at the 20/ oil to black ratio whereas drymilling required two passes through the mill and could only beaccomplished at about one-fourth the rate available from the invention.It should also be noted that the horsepower input to the mill was onlyslightly increased when the carbon black was ground in the presence ofoil and this provided the additional benefit of greatly reducing theenergy requirement for grinding each pound of black.

As previously indicated, the purpose of this experiment was to producean attrited oil furnace black which would serve as a substitute for EPCchannel black in a rubber compound. The ground carbon blacks and EPCblack were thus compounded into rubber according to the followingrecipe:

1 Parts by Weight Natural Rubber 100.00 100.00 100.00 100.00 Dry GroundBlack ll 55.00 10/100 011 to Black 60.00 20 100 Oil to Black 11 65.00Micronex W-6' 55.00 Circosol 41111 10.00 5.00 10.00 Zinc Oxide 3.00 3.003.00 3.00 Stearic Acid 2.50 2.50 2.50 2.50 Santoflex 1.00 1.00 1.00 1.00B-L-E 1.00 1.00 1.00 1.00 Vultrol 0.50 0.50 0.50 0.50 Sulfur 2.70 2.702.70 2.70 Santocure NSR 0.50 0.50 0.50 0.50 MBTS 0.70

EPC black; Columbian Division, Cities Service Co. 2 Napthenic rubberprocessing oil; Sun Oil Co.

Antioxidant; Monsanto Co.

Antioxidant; Uniroyal, Inc.

5 Retarder; H. M. Royal, Inc.

Accelerator; Monsanto Co.

" Benzothiazyl Disulfide accelerator.

After compounding, each of the stocks was cured at 293 F. andstress-strain and other properties of each were then determined. Resultsare shown in Table 2.

TABLE 2 V Dry /100 oil 20/100 oil ground to black to black EPC Carbonproperties Stifi paste 0. A 10. 6 11. 0 10. 7 12. 9 Volatile, percent byWeigl1t 3 1 2. 4 2. 4 6. 6

Rubber properties 20' L-300 modulus 1,060 1, 180 1, 260 1, 350 20tensile stre th- 3, 450 3, 730 3, 730 4, 050 60 L-300 modu us l, 7201,730 1, 650 1, 740 60' tensile strength. 3, 670 3,850 3, 810 3,860 60elongation 530 545 545 530 I00 tensile strength. 3, 050 3, 600 3, 460 3,720 Max. tensile strength. 4, 210 4, 230 4, 030 4, 140 Log R. 4.6 4.24.2 7.1 Dispersion (visual) 6. 5 7. 0 7. 0 5. 3 Rebound (100, cure) 70.4 69.0 68. 1 69. 3 Goodrich heat buildup- 56.0 58.0 57.0 53. 0

Compared to the dry-ground black (Composition 1), the carbon blacksground in accordance with the invention (Compositions 2 and 3) exhibitedbetter dispersion and somewhat higher tensile strength at the 60 and 100minute cures. Compared to'the EPC black (Composition 4), the carbonblacks ground in accordance with the inventionexhibjted comparalestress-strain properties, much better dispersion, lower Log R, aboutequal rebound, and a somewhat slower cure rate.

EXAMPLE [I Using the same vibrating ball mill and operating conditionsas in Example 1., except that the grinding media consisted of 350 lbs.of %-inch steel balls, HAP carbon black having a Stiff Paste OilAbsorption Value of 13.2 gal./ 100 lbs. was ground in the presence of anaromatic (Sundex 8125) and a parafiinic (Sunpar 2100) rubber-processingoil, In each case the blacks were subjected to only one pass through theball mill.

Compared to the results obtained with dry grinding in Example I, thegreatly increased degree and rate of structure reduction which isavailable from the present invention is particularly apparent from table3. When these carbon blacks were compounded into rubber using the sameformulation as in example I, They exhibited comparable tensile strength,much better dispersion, higher rebound and about equal heat buildup,faster cure, and lower Log R, when compared to the EPC black.

In the foregoing experiments, the rubber processing oil was added to thecarbon black before the latter was fed into the ball mill. It will beunderstood that the oil can, of course, be added to the black as it isbeing fed into the mill or even after the black has entered the grindingchamber.

While the invention has been described with reference to particularmaterials, conditions, apparatus, and the like, it will also beunderstood that various other embodiments will become apparent which arewithin the spirit and scope of the invention as defined in the appendedclaims.

We claim:

1. In a process for reducing the structure of carbon black by subjectinga structured carbon black to the attritioning action of a ball mill, theimprovement which comprises attriting the carbon black in the form of adense, powdery mass which is moistened with an amount a rubberprocessing oil which is less than that required for forming a paste ofthe carbon black and continuing the attritioning of the moistened blackuntil the structure thereof has been substantially reduced.

2. The process of claim 1 wherein the proportion of oil to carbon blackis within the range of about 5 to about 100 parts by weight of oil per100 parts by weight of carbon black.

3. The process of claim 1 wherein the proportion of oil to carbon blackis within the range of about 5 to about 50 parts by weight of oil per100 parts by weight of carbon black.

4. The process of claim I wherein the rubber process oil is selectedfrom the group consisting of napthenic petroleum oils, aromaticpetroleum oils, paraffinic petroleum oils, low

2. The process of claim 1 wherein the proportion of oil to carbon blackis within the range of about 5 to about 100 parts by weight of oil per100 parts by weight of carbon black.
 3. The process of claim 1 whereinthe proportion of oil to carbon black is within the range of about 5 toabout 50 parts by weight Of oil per 100 parts by weight of carbon black.4. The process of claim 1 wherein the rubber process oil is selectedfrom the group consisting of napthenic petroleum oils, aromaticpetroleum oils, paraffinic petroleum oils, low molecular weightpolybutenes, and vegetable oils.
 5. The process of claim 1 wherein theball mill is vigorously vibrated for attritioning of the carbon black.6. The process of claim 1 wherein the structured carbon black is anintermediate structure oil furnace black or a high structure oil furnaceblack.